FIG. 1 is an explanatory view showing the conventional method for manufacturing an oxide superconductor disclosed for example in a paper entitled "Manufacture and Evaluation of Ceramics High-Temperature Superconducting Material", Koji Kishidera, Industrial Chemical Engineering, Department of Engineering, Tokyo University published at a symposium entitled "Manufacture and Application of High-Temperature Superconducting Material" on Apr. 6, 1987. As the first step, an oxide of lanthanoid metal and alkaline earth metal and an oxide of copper are weighed (1). The second step is mixing (2) in a mortar, the third step is pre-baking (3) at a temperature of several hundred degrees, the fourth step is crushing and mixing (4), the fifth step is shaping (5) into a desired configuration, and the sixth step is final baking at a temperature from 900.degree. C. to 1100.degree. C.
This method is called the powder mixing method, and one example of the characteristics of the resistance relative to temperature of an oxide superconductor manufactured by this method is illustrated in a characteristic curve 100 in FIG. 2.
In FIG. 2, the axis of abscissa represents temperature and the ordinate represents resistance. The point E is the temperature usually referred to as the onset at which the change in resistance begins to rapidly decrease, and the point F is the temperature usually referred to as the offset at which the resistance disappears.
The change in resistance according to temperature of the oxide superconductor manufactured by the conventional manufacturing method is as shown by the characteristic curve 100, from which it is seen that the temperature difference between the point E of the onset and the point F of the offset is large, making the offset or the temperature at which the resistance disappears low, so that the necessary low temperature becomes even lower and the characteristics of the resulting superconductor are inferior. These considerations pose a problem.